Humic acid modified biochar enhances the degradation of phenanthrene by Proteus sp. GH-2.

Phenanthrene is a typical polycyclic aromatic hydrocarbons（PAHs）pollutant which long-term persistence poses significant hazards to both the environment and human health. The utilisation of microorganisms has been demonstrated to facilitate the effective and environmentally sustainable elimination of PAHs. In this study, a phenanthrene-degrading bacterium, Proteus sp. GH-2, was isolated and identified. To elucidate the degradation mechanism of GH-2 for phenanthrene, we conducted intermediate product analysis using HPLC-MS, revealing that GH-2 degrades phenanthrene via the phthalic acid pathway.Transcriptome analysis results show that the significantly up-regulated genes are mainly enriched in transmembrane transport, redox reaction and energy metabolism. To enhance degradation efficiency, we immobilized the bacteria using humic acid (HA)-modified biochar. FT-IR, XPS, and elemental composition analyses revealed changes in the functional groups and elements of the modified biochar, showing an increase in oxygen-containing functional groups and oxygen content, thereby improving the hydrophilicity of the material. This modification aimed to enhance the adsorption performance of biochar, and SEM further demonstrated that the modified biochar could adsorb more bacteria. When applied to soil contaminated with phenanthrene, the immobilized bacteria achieved an 82.4% total phenanthrene removal within 28 days, which was higher than the 70.8% rate of the free strain. These findings demonstrate the great potential of immobilized bacteria in environmental pollution remediation and provide a potential strain for the bioremediation of PAH-contaminated environments.